I got some warnings when compiling my program (see below). I am using Visual Studio C++ 6 and STLport 4.5.3 I've seen some questions about this issue in the mailing list, but did not get the feeling that I understand what is going on and when I can safly ignore them? Thanks a lot. c:\src\boost\boost\thread\exceptions.hpp(29) : warning C4275: non dll-interface class '_STL::logic_error' used as base for dll-interface class 'boost::lock_error' c:\progra~1\micros~3\vc98\include\stlport\stdexcept(72) : see declaration of 'logic_error' c:\src\boost\boost\thread\exceptions.hpp(35) : warning C4275: non dll-interface class '_STL::runtime_error' used as base for dll-interface class 'boost::thread_resource_error' c:\progra~1\micros~3\vc98\include\stlport\stdexcept(80) : see declaration of 'runtime_error' c:\src\boost\boost\thread\mutex.hpp(37) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::mutex' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\mutex.hpp(75) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::try_mutex' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\mutex.hpp(115) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::timed_mutex' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\thread.hpp(39) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::thread' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\thread.hpp(68) : warning C4275: non dll-interface class 'boost::noncopyable' used as base for dll-interface class 'boost::thread_group' c:\src\boost\boost\noncopyable.hpp(22) : see declaration of 'noncopyable' c:\src\boost\boost\thread\thread.hpp(79) : warning C4251: 'm_threads' : class '_STL::list<class boost::thread *,class _STL::allocator<class boost::thread *> >' needs to have dll-interface to be used by clients of class 'boost::thread_group'